The present disclosure relates to a slot-die coating method and apparatus for manufacturing a patterned coating layer on a substrate. Organic coatings layers are typically applied to a substrate as a liquid solution, e.g. for manufacturing OLED or OPV devices. For many applications, e.g. manufacturing of photo-active layers and/or light-emitting layers, it may be desired to provide one or more homogeneous coating layers on a substrate, i.e. having a homogeneous layer thickness. One technique for manufacturing a homogeneous coating layer may be referred to as “slot-die coating”. This technique typically comprises providing a slot-die coating head arranged over a substrate surface. The slot-die coating head comprises an outflow opening forming a slit that is arranged in a slit direction over the substrate surface. A coating fluid, e.g. supplied by a coating fluid supply, flows through the outflow opening onto the substrate surface. A relative movement between the outflow opening and the substrate surface is controlled along a coating direction. The coating direction is typically transverse, i.e. having a perpendicular component, to the slit direction. In this way a homogeneous layer may be manufactured along a width of the slit onto the substrate surface.
In addition to having a homogeneous coating layer, it may be desired to provide a patterning of the coating on the substrate surface, e.g. wherein the patterned coating comprises coated areas on the substrate surface separated by uncoated areas. For example, for the manufacture of photo-active layers and/or light-emitting layers it may be desired to provide separated active areas on a substrate, e.g. for building an array of photo-cells. Many different methods are known for providing a patterned coating layer, e.g. printing or imprinting techniques such as inkjet printing, rotatory screen printing, gravure printing, offset printing, flexo printing. Unfortunately, in practice these processes do not always provide a desired homogeneity of the coating layer and/or suitability for large scale production, e.g. in a roll-to-roll process. It may thus be advantageous to use a patterning technique that can be combined with a slot-die coating process.
A first option for manufacturing a patterned coating with slot-die coating may be referred to as “in-situ patterning” or “active patterning”, wherein the slot-die coating head is actively used for selectively applying the coating on specific areas of the substrate. In one example, an intermittent transfer is controlled of the coating fluid from the slot-die coating head onto the substrate surface, e.g. by switching a valve between the slot-die coating head and the coating fluid supply and/or selectively removing the slot-die coating head from the substrate. In this way coated areas may be provided having boundaries transverse to the coating direction. Unfortunately, it is found that an intermittent switching of the supply and/or removal and reapplication of the coating head may result in edge effects wherein the coating is no longer uniform e.g. due to the accumulation of coating material on the coating head. For example, U.S. Pat. No. 7,041,336 and U.S. Pat. No. 5,536,313 describe problems with edge effects and propose adaptations to the nozzle to better control the flow-rate out of the nozzle when the flow is interrupted. Disadvantageously, this may lead to a complicated nozzle design.
An alternative method for consideration that could to have as well a uniform leading as a trailing coating edge is to dynamic control a distance between the coating head and the substrate. Therein, the coating head is moved towards a first position, close to the substrate to initiate the coating process at the leading edge of a pattern to be formed. To interrupt the coating process at the trailing edge of the pattern the coating head is moved towards a second position, further away from the substrate. Depending on the properties of the liquid with which the substrate is to be coated the first position is typically selected in a range of 5-250 micron. In the process of coating between the leading edge and the trailing edge the coating head should be held close (e.g. with a tolerance of about 1 micron) to the first position. In addition the positioning of the coating head should be carried out at a relatively high speed. For example, the coating head should be displaced over a distance of 4 mm within 25 ms. In practice it has been found that the combination of these requirements is difficult to realize. Fast movements of the coating head tend to cause vibrations in the coating apparatus that result in relatively large temporal variations in the distance between the coating head and the substrate. This results in non-uniformities in the applied coating.